Which of the following functions is a direct variation?

f(x) = 2x
f(x) = x + 2
f(x) = 2

When two variable quantities have a constant (unchanged) ratio, their relationship is called a direct variation. It is said that one variable "varies directly" as the other...simply when the y-intercept is zero.

So the best answer is f(x)=2x

Can you tell us the question